FreeLists / si-list / [SI-LIST] Re: ESD solution on antenna output

[Ian Barrett <Ibarrett@xxxxxxxxxxxxxx>]

Thanks for all the replies, there seems to be some kind of consensus that
there are better devices than an inductor, and nothing is probably better
too! I will look into the alternatives in more detail, and hopefully gain a
better understanding at the same time.

Ian.


-----Original Message-----
From: Sandor Daranyi [mailto:sandord@xxxxxxxxxxxxx]
Sent: 03 February 2004 01:10
To: Ibarrett@xxxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ESD solution on antenna output


Hello Ian,

There are ESD suppressor components offered for RF applications, but of
course they are highly dependent on the frequency, power, impedances etc.
involved. These parameters were not detailed in your post, so with a stab in
the dark for a small device with not very high frequency, there might be a
relevant device at 
http://www.spkecl.com/htdoc/over-voltage-protector-ESD-Guard.htm or there
are other similar offerings from Littelfuse or Bussmann and others.

...but this wasn't your question.  You hinted at having a solution yourself,
which involves removing the inductor.  I have to agree.  It's always tricky
to make a meaningful comment without knowing the details (and I'm not an
expert), but I don't see how the inductor could provide an ESD solution in
that configuration, unless the frequency of transmission is very high and it
is guaranteed that there is not much ESD energy at frequencies approaching
that.  Ever.

The noteworthy thing is that the most likely failure mode of the inductor is
open, which might keep the device operating, but it can then be (perhaps
fatally) damaged by the next serious ESD event that comes along.

What actual (physics based) explanation has your colleague offered for the
inductor, apart from that all ESD experts use it?  It suspiciously sounds
like it is something that is appropriate under some specific circumstances,
and has then been applied because "experts do it".  People can get touchy
when they are asked about something they've done that they don't totally
understand why...  Of course, we never see that on this forum!!!  ;-)

Regards,

Sandor Daranyi
Senior Design Engineer

Ian Barrett wrote:
> I am currently having a lively discussion with a colleague about an ESD
> problem we have encountered. The trouble is I don't think either of us 
> know
> enough to be able to convince the other of our point of view.
>
> The product is a small radio transmitter that is very susceptible to 
> an ESD
> spike applied directly to it's antenna. The design includes a small 
> inductor
> between the antenna output and ground. My colleague (the designer) put it
> there to try and alleviate any potential ESD problems. I have found 
> that I
> cannot solve the ESD susceptibility problem without removing it.
>
> He claims 'any ESD experts will tell you to place this inductor' and 
> wants
> me to try and find another solution to the problem. But I think the 
> inductor
> is making the situation worse by coupling the ESD spike onto the ground
> plane.
>
> Can anyone offer some theory to back up either argument?
>
> Ian.


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